Extend XQXQ module functionality by exposing the prolog

[Sorin Marian Nasoi]

adding the following two functions to the XQXQ module should allow for an arbitrary static context to be set up as required (e.g. declaring namespaces, enabling the hof option, ...).
Hence, it should not be required anymore to make changes to the original query.

 declare %ann:sequential function prepare-library-module(
 $library-module-text as xs:string,
         $prolog as xs:string ) as empty-sequence() external;

 and

 declare %ann:sequential  function prepare-main-module (
 $main-module-text as xs:string,
         $prolog as xs:string ) as xs:anyURI external;

 The $prolog parameter can be an arbitrary XQuery prolog that is used to
 populate the
 static context of the module to be compiled. To do this, the
 StaticContext::loadProlog
 function of the C++ API can be used.